Droplet detector and euv light generation device

Abstract

A droplet detector preferably includes: an application unit configured to emit a pulsed beam at a predetermined cycle and apply a plurality of pulsed beams to a droplet moving in a detection region on a trajectory; and a light receiving unit configured to receive a scattered pulsed beam that is generated from the plurality of pulsed beams applied to the droplet and scattered by the droplet.

What is claimed is: 
     
         1 . A droplet detector comprising:
 an application unit configured to apply, to one droplet moving in a detection region, a plurality of pulsed beams at a predetermined cycle; and   a light receiving unit configured to receive a plurality of scattered pulsed beams, the plurality of scattered pulsed beams being generated by scattering, at the one droplet, the plurality of pulsed beams having been applied to the one droplet.   
     
     
         2 . The droplet detector according to  claim 1 , wherein
 the application unit and the light receiving unit are placed in a plane orthogonal to a trajectory of the one droplet and placed at positions different from positions facing to each other across the trajectory.   
     
     
         3 . The droplet detector according to  claim 1 , comprising
 a beam splitter configured to transmit the pulsed beam applied from the application unit and reflect the scattered pulsed beam propagating toward an optical axis of the pulsed beam applied from the application unit, in the scattered pulsed beam scattered from the droplet moving in the detection region, wherein   the light receiving unit receives a scattered pulsed beam reflected off the beam splitter.   
     
     
         4 . The droplet detector according to  claim 1 , wherein
 the application unit includes   a mode-locked laser, and   an illuminating optical system configured to shape a pulsed beam emitted from the mode-locked laser in a manner that the pulsed beam is shaped in a sheet-like pulse beam in the detection region.   
     
     
         5 . The droplet detector according to  claim 1 , wherein
 the light receiving unit includes   a photodetector configured to subject the scattered pulsed beam to photoelectric conversion, and   a light receiving optical system configured to guide the scattered pulsed beam to the photodetector.   
     
     
         6 . An extreme ultraviolet light generating apparatus comprising:
 an application unit configured to apply, to one droplet moving in a detection region, a plurality of pulsed beams at a predetermined cycle;   a light receiving unit configured to receive a plurality of scattered pulsed beams, the plurality of scattered pulsed beams being generated by scattering, at the one droplet, the plurality of pulsed beams having been applied to the one droplet;   a laser unit configured to emit a pulsed laser beam; and   a controller configured to output, to the laser unit, a signal that gives a trigger to the laser unit to emit a pulsed laser beam in a manner that the pulsed laser beam is applied to the one droplet, when the one droplet detected in the detection region reaches a plasma generation region after received light intensity at the light receiving unit is changed.   
     
     
         7 . The extreme ultraviolet light generating apparatus according to  claim 6 , wherein
 the controller detects a value at a predetermined ratio to largest received light intensity at an interval corresponding to a period of a mode-locked laser included in the application unit, based on an envelope of received light intensity indicated by a plurality of pulse signals inputted from the light receiving unit, and   the controller delays a signal generated based on a pulse signal closest to a time point at which the envelope exceeds the value by a predetermined period to form a signal that gives a trigger to emit the pulsed laser beam to the one droplet.   
     
     
         8 . The extreme ultraviolet light generating apparatus according to  claim 6 , wherein
 the application unit includes
 a mode-locked laser, and 
 an illuminating optical system configured to shape a pulsed beam emitted from the mode-locked laser in a manner that the pulsed beam is shaped in a sheet-like pulse beam in the detection region, 
   the laser unit includes
 a prepulse laser unit configured to apply a prepulsed laser beam, and 
 a main pulse laser unit configured to apply a main pulsed laser beam, and 
   the prepulse laser unit generates the prepulsed laser beam using the mode-locked laser as a seed light source.   
     
     
         9 . The extreme ultraviolet light generating apparatus according to  claim 6 , further comprising
 a target supply unit configured to output the one droplet, wherein   the application unit is placed in a manner that the detection region is located on the target supply unit side of the plasma generation region.   
     
     
         10 . An extreme ultraviolet light generating apparatus comprising:
 an application unit configured to apply, to one droplet moving in a detection region, a plurality of pulsed beams outputted from a mode-locked laser at a predetermined cycle;   a light receiving unit configured to receive a plurality of scattered pulsed beams generated by scattering, at the one droplet, the plurality of pulsed beams having been applied to the one droplet;   a prepulse laser unit configured to emit a prepulsed laser beam using the pulsed beam as seed light; and   a controller configured to output a signal that gives a trigger to the prepulse laser unit to emit the prepulsed laser beam in a manner that the prepulsed laser beam is applied to the one droplet when the one droplet detected in the detection region reaches a plasma generation region after received light intensity at the light receiving unit is changed.   
     
     
         11 . The extreme ultraviolet light generating apparatus according to  claim 10 , wherein
 the application unit includes an illuminating optical system configured to shape a pulsed beam emitted from the mode-locked laser in a manner that the pulsed beam is shaped in a sheet-like pulse beam in the detection region.   
     
     
         12 . The extreme ultraviolet light generating apparatus according to  claim 10 , further comprising
 a main pulse laser unit configured to emit a main pulsed laser beam, wherein   the controller outputs a signal that gives a trigger to the main pulse laser unit to emit the main pulsed laser beam in a manner that the main pulsed laser beam is applied to a dispersed target substance dispersed from the one droplet to which the prepulsed laser beam has been applied.   
     
     
         13 . The extreme ultraviolet light generating apparatus according to  claim 10 , further comprising
 a target supply unit configured to output the one droplet, wherein   the application unit is placed in a manner that the detection region is located on the target supply unit side of the plasma generation region.